The present invention relates to scheduling serial message transmissions on a bus. More specifically, the present invention is related to such systems which utilize a single bus and wherein rescheduling of the message transmission order must be efficiently implemented.
In some message transmission systems, it is required that messages be retained after transmission in case a faulty transmission/reception of the message occurred. In the event of such a fault, then the message must be scheduled for retransmission. Also, generally message transmission systems require scheduling in accordance with message priority, and, therefore, reception of a new message of a higher priority requires the efficient rescheduling of all messages which remain to be sent so as to transmit the messages of higher priority first. Such systems can correspond to the American Truck Association (ATA) system J1708 which is a system recommended for serial data communications between microcomputer systems in heavy duty vehicle applications.
In systems such as those discussed above, typically it is undesirable to have to physically move any message stored in memory in the event that a new message has been received which requires transmission prior to the previously-stored message. In other words, any systems which require moving actual stored messages in order to implement reprioritization of messages waiting to be sent is an undesirable system since this would require extensive time to implement such message movement in memory. In addition, typically systems require the feature of saving messages which have been sent in case faults are subsequently detected which will require the retransmission of this message. Systems which implement this by utilizing buffer memory to store each message after it is sent are undesirable because of the consumption of additional time required for such message storage and the requirement for additional memory space. In addition, the function of locating the message to be retransmitted in the event of a fault is generally time-consuming in prior systems since all messages which were previously sent are searched in a generally inefficient manner.